This project will extend analysis of the central and reflex mechanisms controlling the production of adaptive, rhythmic patterns of motor output in Limulus. The major motor patterns under study control the ventilatory (respiratory) rhythm and rhythmic chewing movements in feeding. The gill ventilatory rhythm is under predominant central control. Control of chewing movements is more complex, with evidence favoring an interaction of reflex and central elements of pattern generation. The principal questions for study will be: (1) How do central and reflex mechanisms interact in controlling patterns of rhythmic motor output? (2) What is the cellular nature and mode of action in motor control of central neural oscillators? (3) What is the behavioral significance and mode of activity of command fibers? (4) How are decisions or choices between stereotyped behavior patterns made within the central nervous system? I will record extracellular activity of motoneurons and muscles during both passive and active movement of gill plates of leg coxae. Natural chemosensory input and stimulation of defined command fibers will be used to elicit active ventilatory movement in intact, selectively deafferented, and totally deafferented preparations. I will also record intracellular activity from identifiable motoneurons and premotor interneurons, and hopefully from oscillator and decision elements in the isolated segmental ganglia and brain. The results of the project will characterize the major features of the elements controlling these rhythmic behavior patterns in Limulus.